Valving systems are used with various containers, such as chemical storage tanks, vehicle fuel tanks and the like, for regulating the discharge of pressurized gases or vapor from the container, such as when the container temperature becomes elevated or during filling. In addition, valving systems have been used on such containers for relieving vacuum conditions therewithin when the pressure within the container becomes excessively low in relation to the atmospheric pressure. In some applications, a separate valve assembly is used for regulating the discharge of pressurized vapor from the container, and another independent valve assembly is used to relieve excessive vacuum in the container. Using separate valve assemblies to perform the two separate functions is expensive. In addition, such a system doubles the potential for leakage problems in the areas of the valve assemblies which normally are mounted within ports formed in the container walls.
Therefore, various valve assemblies have been designed as a combination pressure and vacuum relief vent device which provides both high flow rates of pressure relief as well as negative pressure or vacuum relief, all through a single port in the container wall. Such combination valve assemblies are considered "two-in-one" pressure and vacuum relief vent devices. They normally are self actuating. In other words, the device opens to provide high flow rates for pressure relief and closes when the pressure falls below a given amount. Vacuum relief is provided at a predetermined or set negative pressure or vacuum condition and allows a relatively high flow rate of make-up air to enter the container, such as during emptying or reductions in ambient temperatures.
When comparing the separate valve systems with the "two-in-one" valve assemblies, the separate valves, individually, were more simple and reliable, but that very factor has been a continuing problem with "two-in-one" valve assemblies in other words, a combination pressure and vacuum relief vent device may be less expensive to manufacture and install than two separate pressure and vacuum relief valves, but the very combination of the two functions in a single device renders the two-in-one valve assembly quite complex. Prior combination valve assemblies incorporate an unduly number of moving pans which are prone to damage, wear and/or malfunctioning. The present invention is directed to solving these problems by providing an extremely simple combination pressure and vacuum relief vent valve assembly which includes a minimum number of parts and includes a number of features not heretofore available.